The present invention relates to a detector for controlling the operation of a suction pump arranged to pump liquid when the level of liquid reaches a predetermined upper limit and to stop as soon as the level falls to a predetermined lower limit.
Detectors for controlling pumps are known which comprise floats or elements subjected to the thrust of the liquid. As the result of wear, corrosion or possible blockage by foreign bodies, the operation of such detectors is not reliable. Moreover, they are practically useless in mobile installations which may be subjected to considerable inclinations, such as boats or floating platforms.
The present invention does not use any movable element displaced by the liquid which is to be pumped. Instead, the invention utilises, fixed electrodes forming part of an electric control circuit for the pump. Electrode type detectors are also known and examples are described in German Patent Specification Nos. 500,203 and 1,273,443, and French Patent Specification Nos. 1,256,197 and 1,562,012. The known detector which is closest to that of the invention is described in French Patent Specification No. 1,256,197. However, this known detector is designed and connected to an electric circuit for the purpose of maintaining the level of a liquid between two fairly close limits in order to ensure adequate filling of a tank.
The present invention seeks to eliminate as far as possible a liquid which has penetrated into a vessel and has risen to an unacceptable level; in addition, the invention makes it possible to obtain the clean stopping of the pump when the level of liquid has reached a predetermined lower limit. Such a clean stoppage cannot be achieved with the detector of the abovmentioned French Pat. No. 1,256,197.
One particular use for a detector of the invention is the control of a bilge pump in a ship; the liquid to be pumped out is very often seawater, which is a good conductor of electricity and with which up to the present time it has been practically impossible to obtain clean stopping of the pumping because the slightest wet layer between the electrodes is sufficient to join them electrically and to cause the pump to operate.